Uncovering Role of Symbiotic Fungi in Soil Carbon Storage
Mycorrhizae inhabiting plant roots have major impact on carbon release rates.
The Science
Soil is the largest reservoir of carbon in the terrestrial biosphere, containing more than the amount found in the atmosphere and vegetation combined. If soils were to lose even a small fraction of their carbon, Earth’s climate could shift rapidly, with such changes having important repercussions for U.S. policies on, for example, food security and coastal inundation. Identifying the factors that control gains of soil carbon at local to global scales has been difficult. However, researchers supported by the U.S. Department of Energy (DOE) have demonstrated that mycorrhizae—fungi that establish symbiotic relationships with plant roots—control the quantity of carbon in today’s soils.
The Impact
Importantly, this research links the traits of mycorrhizae to soil carbon storage at the global scale—from tropical forests to the far northern reaches of boreal forests. In their analysis, researchers found that the effect of different mycorrhizal types on soil carbon pools was of far greater consequence than impacts associated with an ecosystem’s productivity, climate (i.e., temperature and precipitation), or the physical properties of its soil (e.g., clay content). Whether climate change alters the distribution of these different fungal species remains to be seen, but increases in the abundance or geographical spread of one fungal type—arbuscular mycorrhizal—may portend a significant, biologically controlled positive feedback to the climate system.
Summary
Using global datasets, researchers found that soils dominated by ecto- and ericoid mycorrhizal fungi contain ~70% more carbon than those dominated by arbuscular mycorrhizal fungi. Although the mechanism underlying the difference in soil carbon storage is still debated, competition for nitrogen between plants (via their fungal symbionts) and other free-living decomposers in the soil appears to provide the best answer. Ecto- and ericoid mycorrhizal fungi produce many different types of enzymes released into the soil to unlock the nitrogen bound to soil carbon pools. These fungi are also very effective competitors for nitrogen, making this nutrient scarce for other carbon decomposers in the soil and consequently reducing their biomass and rates of decomposition. By contrast, arbuscular mycorrhizal fungi lack many of these enzyme systems, and rates of soil carbon decomposition thus are more rapid.
Contact
Colin Averill
University of Texas at Austin
Funding
The Center for Tropical Forest Science and the Smithsonian Institution Global Earth Observatory provided funding for the collection and analysis of soil profile data at large forest dynamics. This work benefited from extensive data contributions to the International Soil Carbon Network from the U.S. Department of Agriculture’s Natural Resources Conservation Service and National Cooperative Soil Survey and from the U.S. Geological Survey. Support was provided by a fellowship from the University of Texas at Austin and the National Science Foundation (NSF) Graduate Research Fellowship Program (grant DGE-1110007). Additional funding provided by NSF grant number DEB 07-43564 and DOE grants 10-DOE-1053 and DE-SC0006916.
Publications
Averill, C., B. Turner, and A. C. Finzi. “Mycorrhiza-mediated competition between plants and decomposers drives soil carbon storage,” Nature 505, 543–545 (2014). [DOI: 10.1038/nature12901].
Highlight Categories
Performer: University
Additional: Collaborations , Non-DOE Interagency Collaboration
